If you visit the National Slate Museum in Llanberis, Gwynedd, you can watch slate- makers splitting apparently solid blocks of stone into slates using nothing more than a wooden hammer, a broad chisel, and a lot of skill. Every time you think they cannot possible get a thinner piece, they split the slate again.
These thin sheets of stone make the ideal roofing material: they are easy to transport, can be cut into a variety of shapes, and, being lighter than other forms of stone tile, they do not need such substantial roof timbers or such a steep roof pitch to support them.
Roofing the world
Taking advantage of this fine-grained metamorphic rock, the slate-makers of North Wales can claim to have ‘roofed the world’. Half the buildings in New York were once kept dry using Welsh slate, as was the Governor’s Palace at Williamsburg in Virginia. The decorative properties of differently shaped and coloured Welsh slates were greatly appreciated by the builders of the dome of the Royal Exhibition Building in Melbourne, Australia, built in 1879. It was the roofing material of choice for the huge number of terraced houses built in cities such as Liverpool, Bristol, London, and Dublin during the 19th and early 20th centuries. Those same Victorian and Edwardian houses probably have a damp-proof course of Welsh slate.
